Apparatus for measuring flows of fluids



2 Sheets-Sheet 1 MM: "Mime Ila/2mm R. O. PERRINE APPARATUS FOR MEASURING FLOWS OF FLUIDS Filed March 4, 1932 Nov. 14, 1933.

Nov. 14, 1933.

R. o. PERRINE APPARATUS FOR MEASURING FLOWS OF FLUIDS Filed March 4, 1932 2 Sheets-Sheet 2 MAY/Mr v p 3) MV- gem/v Mkcmwzx iiiiili. I T: at. '1 HULK J. I. g .I J\ v 2 3 l Patented Nov. 1"4,"l 93 3 v 2' i; 2 I 2 UNITED-STATES PATENT OFFICE APPARATUS FOR MEASURING FLOWS or f FLUIDS Robert 0. Perrine, MilwaukeefWisl, assignor to Cutler -Hammer, Inc., Milwaukee, Wis., a corporation of Delaware 7 Application March 4, 1932; Serial No. 596,746

' "9 Claims. (o1.; 73- -1's7) This invention relates to improvements in apconduit 10'is a relatively large capacity meter of paratus for measuring flows of fluids. a well known type. As shown'I prefer to employ It is customary in systems of the character an electric fluid meter of the general character herein contemplated to employ within the fluid disclosed in Thomas Patent No. 1,222,492, dated 1 r conduit a meter of relatively large capacity which April 10,1917. In accordance with the teachings will function to accurately measure the flow of of said Thomas patent a variable amount of heat fluid so long as the volumetric rate of flow exis supplied to the flow of fluid in conduit ceeds a predetermined relatively large value. through the medium of an electric heating ele- When the volumetric rate of flow decreases to. a ment 11 to thereby provide a substantially con- ;10 relatively low value such large capacity meter stant'rise intemperature of the fluid between 65 is inherently incapable of functioning to acthermometer resistances 12 and 13 such curately measure the flow. in temperature being predetermined by the 7 It is therefore one of the objects of my invenvalue of the temperaturedifference resistance 14 tion to provide an apparatus for accurately measwhich is likewise preferably located within the 15 uring the fluid flow notwithstanding extremely stream of fluid. As shown'the resistance ther- 70 Wide variations inthevolumetric rate of flow. 'mometer 12 and temperature difference resist Another object is to provide an apparatus ance 14 are connected to form one arm of a wherein a relatively 'small capacity meter of a Wheatstone bridge, resistance thermometer 13 positive displacement type is automatically renforms another arm of the bridge, and fixed resist- ;dered solely effective for measuring the flow when ances- 15, 16 form the other two arms of the 75 the volumetric rate thereoflfallsi below a predebridge. [A galvanornetercoil 17 is connected termined value. n across said bridge in the usual manner,the it Another object is -to'provide.. an apparatus needle 18 of the galvanometer being deflectable in wherein the meter of v relatively large capacity is a sense and to a degree corresponding to the deautomatically rendered 'efiective or inefiective for gre'e of unbalancing of the bridgecircuit incident measuring the flow in response to variations in the to variations in the volumetric rate of flow of volumetric rate of such flow., 1 i the fluid.

Anotherobject 'isto provide a novel system A ratchetingfdevice 19 of the character disfor effecting measurement of thefluid flow whereclosed in Leeds Patent No. 1,125,699,'dated J an- 30 in continuation of the flow isinsured during tranuary 19, 1915 is subjected to control in a well sition of the measurement control from the meter known manner by the needle 18. Said ratcheting of relatively large, capacity to the meter of reladevice comprises in general a continuously opertively small capacity, and vice versa. able electric motor 20 which drives a shaft 21 Another and more specific object is to provide carrying cams 22 and 23 having associated "35 a fluid flow measuring system utilizing a relaclutchelements so arranged that the shaft 24 tively large capacity meter of the electric 'heatremains stationary so long as needle 18 is in an exchange type and a relatively small capacityjintermediate or neutral position, whereas upon meter of the positive displacement type. deflection of needle 18 in one direction or the Otherobjects and advantages of'the invention other shaft 24 is moved intermittently in'a corre- 40 will hereinafter appear. v sponding direction, Connected with shaft 24 The accompanying drawingsillustrate certain through suitablegearing 25, is a contactor 26 embodiments of the inventionwhich will now be forming .a part of the adjustable rheostat 27, described; it being understoodthat the embOdiwhich as shown is.connected'in serieswith the ments illustrated are susceptible of modification heating element 11. Thearrangement is such 45 in the details of construction and'operation there'- 7 thatvupon increase in'the volumetric rate of flow of within the scope of the appended claims. of'fluid inconduit' 1O contactor 26 is moved step- In the drawings,- Figure 1-is a schematic and by-step inja clockwise direction to gradually exdia r mm i illustration of I. 0 r01 ys m clude resistance from the circuit of element 11 embodying y invention,'and whereby thevalue of current supplied to and the 0 Fi 2 is a Similar i lust ation of a modified amount of heat generated by the latter is in form o COIltrOl System bo y ngmyiinvention. creased. In likemanner. upon a decrease in the R f rrin fir t Fi 1', h n meral 10 desigvolumetric rate of flow. of fluid contactor 26 is nates a main conduit through which a fluid (such moved step-by-step in a counterclockwise direc- V as combustible gas) is adapted toflow from any tion'to increase the value of resistance'27 in cirsuitable source (not shown). lLocated'within cuitiwfith element 11. The amount of heatsupllo plied by element 11 is thus increased or decreased directly in accordance with variations in the volumetric rate of flow of the fluid.

An integrating wattmeter 28 is provided-the same having its voltage coil connected in parallel with element 11, as indicated by terminals 28 and having its current coil-connected in series with said element, as indicated by terminals 28*. Wattmeter 28 thus operates in a well known manner to register in accordance with the total amount of energy supplied to element 11, and said wattmeter is calibrated to indicate directly the total volume of the fluid measured by the electric fluid meter.

Assuming that the electric fluid meter aforeclescribed has a capacity for accurately measuring a flow of fluid having amaximunrvolumetric rate of flow of 100,000 cubic feet per hour, it will be understood that if the volumetric rate of flow decreases to a relatively smallvalue, say, below 3,000 cubic feet per hour, such meter will not function as accurately as a meter of the positive displacement type. Accordingly, I providewithin conduit 10 a valve 29 to be operated to anopen or closed position selectively by means of an electric motor 30. Communicating With conduit 10 on opposite sides of valve 29 and arranged to by-pass the latter is a relatively small or branch conduit 3l,the same having interposed therein a relatively smaller gate valve 32 to be operated to an open or closed position selectively by means of an electric motor 33. Also interposed in branch conduit 31 at the outlet side of valve 32 is a meter 34 of the positive displacement type,and it may be assumed that meter 34 has a maximum capacity of, say, 5,000 cubic feet per hour.

The elements now to be described are so arranged that upon' a decrease in the volumetric rate of flow of fluid in conduit 10 to a value below, say, 3,000 cubic feet per hour the valve 32 will be operated automatically to effect full open positioning thereof and valve 29 will thereupon be operated automatically to effect full closed positioning thereon-the voltage coil circuit of wattmeter 28 being interrupted to render the electric fluid meter ineffective for measuring the flow.

Under the conditions last mentioned, meter 34 will of course be rendered solely effective for measuring the flow of fluid. Although wattmeter 28 is rendered ineifective for registering the flow of fluid under these conditions, it will be noted that the other elements of the electric fluid meter remain active and responsive in the usual manner to variations in the volumetric rate'of flow of the fluid. Thus upon an increase in the volumetric rate of flow of fluid to, say, 4,000 cubic feet per hour, or more, the control mechanism will function automatically to effect full open positioning of valve 29 and subsequent full closed positioning of valve 32,-the voltage coil circuit of wattmeter 28 being closed simultaneously to render the electric fluid meter solely effective for measuring the fluid flow. As aforeindicated the electric fluid meter will remain solely effective for measuring the flow when the volumetric rate of the latter is within the range of 100,000 and 3,000 cubic feet per hour, and the positive displacement meter 34 will remain solely effective for measuring the flow when the volumetric rate thereof is within the range of zero to 4,000 cubic feet per hour. The overlap of the'ranges thus other, as will be obvious.

More particularly, it will be noted that I have provided a shaft 35 which is connected for angular movement jointly with the rheostat contactor 26,-said shaft having fixed thereto a disk 36 having a relatively wide peripheral notch 36 located in a definite angular position with reference tocontactor 26. Looselymounted on shaft 35 closely adjacent to disk 36, and having a limited oscillatory movement with respect to the latter, between stops 36 and 36 is a member 36 which is arranged to overlie different portions of the notch. depending upon the direction of rotation of contactor 26 and disk 36 associated therewith. Located adjacent to disk 36 is apair of contacts 37, 3'7 ,the contact 37 being biased away from contact 3'7 to permit separation of said con tacts when the cam projection 3'7 enters the notch 36 ,--said projection 37 being engageable with the periphery of disk 36 and with member 36 under given conditions to maintain contacts 37 3'7 in engagement with each other.

responding direction to such a degree that projection 37 will be permitted to enter the notch 36 on the left-hand side of member 36 as shownin full lines. Contact 37 will therefore disengage contact 37 to interrupt the energizing circuit of coil 38 of a relay 38. The contacts 38 38 of gizing circuit for the fleld winding of motor 33(which is of the split-field type) whereby the latter is operated in a direction to cause full open. positioning of valve 32,--said circuit extending from line L by conductors 46 "and 4'7 through the armature of motor 33, conductor 48 through said field winding 45, thence through said contacts 39 and by conductor 49 to line L Also itwill be noted that with the contacts 41 41 of limit switch41 in the closed position illustrated a short circuit is provided forthe operating coil 50 of a relay 50, said short circuit extending from line L by conductors '40 and 51 through said contacts 41, 41 conductor 52 through coil 50 and by conductors 54 and 46 back to line L Upon full open positioning .of valve 32 the traveling nut 55 associated with.

the operating motor 33 will engage the lug 41 carried by said limit switch 41 to effect opening of the'contacts 41 41 and 41,41 of the latter. Opening of contacts 41 41 results in de-energization of relay 39 with consequent opening of contacts 39 of the latter for interruption of the aforedescribed circuit of motor 33. Opening of contacts 41 41 of switch 41 results in interruption of the aforedescribed short circuit of coil 50 of relay 50. An energizing circuit is thus provided for said coil,-said circuit extending from line L by conductors 46, 54 and 53 through said coil 50 conductors 52 and 56 through a suitable protective resistance 57, to line L v Contacts 50 of relay 50 when closed complete an energizing circuit for the operating-winding and by conductor 58 59 of re1ayi59,-said circuit'extending from line L by conductors 46, 60 and 61 throughthe contacts 62 6280f a limit switch 62- associated with motor 30, conductor 63 through saidwinding 59 conductor I 6 through said contacts 50 con- "ductor fifithrough contacts 38? of} relay 38, and

by"conduc'tor-44 to Iine L Contacts 59 of relay 59, when closed complete an energizing circuit for the field winding 65 of motor (which is also of thesplit-field type) whereby the latter 'i's operatedin a direction to cause full closed positioning of valve 29,-said circuit extending terru'pt the circuit of motor 80-.

from line L by conductors 46, and 67 through the armature of said motor, conductor 68 through conductors 69 and 5,8.to line-L During closure of valve 29, the traveling nut 70 is moved out of engagement with projection '71 said field winding. 66-and contacts 59', and by g to permit closure of the contacts '71, li and 7-1", 7l 'ofga limit switch 71 and to finally engage proje'ction 62 of a limit switch 62 whereby the contacts 62?, 62 of the-latter are disengaged to in- Upon jopenin'g of the contacts 38 of'relay 38 in themanner aforedescribed the circuit of the voltage coilfof wattmeter 28 isbroken thus rendering the latter incapable of registering the flow of fiuid as measured-by the electricflui'd-meter.

{Associated with motor 33 is a relay '72 the operating coil 72* of which is provided-with an "energizing circuit which may betracedtrom line L by conductors '13 and 74 through said coil, and

.througha protectiveres'istance 75 andconductor '76 to line L Relay ,72 is provided with a 'set of normally open contacts 72" which are adapted when closed to pre-set an energizing circuit for the winding '77 of a relay 77, said circuit to be completed fupon concurrent closure of "the contacts 78 78 of limit switch '78 and contacts 38 of relay 38-. As aforedescribed, however, contacts 88 will be opened'due to de-energization of" coil 38*" prior to*closure of contac'ts- 78 '78 of limit switch 318 when valve-32 is'beIng'moved to full open'po'si'ti'on.-- .lVlToreover,

'iti's to be noted that upon subsequentmovement of valvej29 to closed position thecontacts 71,-' 71 of limit switch 71 will be" closed automatically to provide a short-cireiiit for de-energi'zir'ig 'coil '72 of relay '72 pending re-opening ,ofsaid'valve 1 P 29 in the manner hereafter described. Said short "73 and '74 through said'coil conductor 79, 'con tacts 71 71, and by conductors: 80, 67; 80

circuit may be traced from line L jby conductors and46 back'to line L 7 1 With valve 32 fullyopened and valve 29 fully closedin, the manner'aforedescribed to render meter 34 solely effective for measuring the flow (the electric fluid meter being rendered ineffective through interruption of the wattmeter voltage-- coilc'ircuitthrough opening of contacts 38 of relay 38), it is to: be noted that the other'elements of the electric fluid: meterremain active, andothe same will respond to vari'ations in'the volumetric rate of flow of the fluid;- Thus: upon an'increasein the volumetric rate'of flow to, say;

4,000 cubic feet per hour, the el'ectric'fiui'd meter elements will cause automatic movement 'of contactor 26 in a clockwise direction to correspond inglyincrease therate of electrical energysupply to heater elementll. Moreover, due tdthe' re:

verse movement of disk-36; the member 36 will be permitted to move to its dotted line position against'thestop 36, whereby a predetermined degree of angular movement of contactor 26' is permitted prior to' reclosure of contacts 37 37.

Upon closureof'said contacts 37, 3'7 acircuit' across lines L L? is completed for the operating coil 38 ofrelay 38,said circuit being obvious. Resultantclosure ot'contacts 38 ofrelay 38 provides an energizing circuit for the operating coil 81 of relay 81, said circuit extending from l'ne-L by conductors 46, 60, 67 and 82 through contacts 71, 71 of limit switch'll (which is then in closed position), conductor, 83- through said coil-81 conductor 111, contacts 38 and conductor 44' to'line L 1 Contacts 81*" of relay 81 are thereupon closed to complete'a circuit for the field winding 84 of motor 30 whereby valve 29 is moved in the reverse direction to its full open position,said circuit extending from 'lineL by conductors 46, 60 and 67fthr0ugh the'armat'ure of motor 30, conductor 68 through said field winding 84, through said relay contacts 81', and by conductors 85, 69 and.58-to line L Upon'full,

openpositioning of valve 29 nut 70 will have engaged projection '71 of limit switch 71 to cause opening of its contacts 71 71 whereby relay coil 81 is de-energized and the contacts '81 -thereof.

opened to'stop motor 30. At the same time contacts 7'1", 71 of limit "switch '71 willobe opened to interrupt the short circuit'of relay coil 72 and the contacts 72 of relay '72 will close to' complete a circuit for relay coil l'7' ,--"-which circuit'may be tracedfrom line L} by conductor 73 through contacts 78 78 'of limit switch 78 (which is then in closed position) conductor 86 through said coil 77, conductor 8'7, relay contacts '72,

conductor 88, relay contacts 38 44 toline L 7 Contacts 7'7 of relay-77 thereupon close to complete a circuit for effecting operation of-motor 3-3 in a reverse direction, said circuit extending from line L by conductors 46, 54 and 4'7 and conductor through the armatureof motor'33', conductor 48 through the other field winding" 89, relay contacts 7'7", andbycon'ductors 9O and'lfito line L Valve {82 is thus-moved to its fully closed position, whereupon the traveling 'nut-55'engages the projection '78 oflimit' switch 78 to effect opening of contacts 78%, 78*, thus de-energizing relay coil '77 withconsequent opening of relay contacts '7'? for interruption of the circuit of motor 33.

i -As a result of the aforedescribed cycles of operation the several parts of'the control system are returned to the positions thereof illustrated,it

being understood that rheostat contactor 26 is moved to different angular positions to vary the I 'which event the elements are operable automatically in the manner aforedescribed to'first effect full open positioning of valve 32 and subsequent full closed positioning of valve- 29.

The aforedescribed' arrangement whereby the parts of the electric fluid meter are maintained responsive to variationsin the volumetric rate of flow of fluid, while'thepositive displacement meter is rendered solely 1 effective for, measurement of'the-flotwhas the advantage that the electric fluid meter'is always immediately responsive *toaccurately measure theflow when control of the measurement thereof is transferred from meter 34 to the electric fluid meter. Moreover, such an arrangement provides simple and accurate means for controlling and insuring transfer of the measurement control from each flow meter to the other.

If desired a manually operable switch 91 may be provided for interrupting theenergizing circuit of heater element 11 at will,thus rendering the electric fluid meter entirely unresponsive to variations in the volumetric rate of flow; a master switch 92 being also provided to permit disablement of the entire system. Assuming that lines L L are connected with a source of alternating current, a rectifier system 93 of well known form will be provided to insure a proper supply of unidirectional current to the Wheatstone bridge circuit.

The modified form of fluid measuring system illustrated in Fig. 2 is in many respects similar to that illustrated in Fig. 1, and like parts in the two figures have been given like characters of reference. In the device of Fig. 2 the necessity for a valve in the branch conduit 31 has been eliminated, and the positive displacement meter 34 is therefore rendered effective at all times to 7 measure at least a portion of the fluid flow,the

arrangement being such that upon a decrease in the volumetric rate of flow to below, say, 3,000 cubic feet per hour the valve 29 is closed automatically to render the meter 34 solely effective for measuring the flow, and thereafter upon an increase .in the volumetric rate of flow to above, say, 4,000 cubic feet per hour. the valve 29 will be automatically re-opened and the electric fluid meter rendered effective for measuring at least the major portion of the flow.

Thus assuming the electric fluid meter to have a maximum capacity'for measuring 100,000 cubic feet of fluid per hour and the positive displacement meter 34 to have a maximum capacity for measuring approximately 5,000 cubic feet of fluid per hour, and further assuming a presentvolumetric rate of flow of about 60,000 cubic feet per hour (as represented by the relative position of contactor 26 of rheostat 27) it will be understood that valve 29 is in fully open position (as indicated by the position of traveling nut and that the electric fluid meter and the positive displacement meter are each functioning to measure a portion of the total fluid flow.

Upon a decrease in the volumetric rate of flow to, say, below 3,000 cubic feet per hour the contactor 26 will have been moved in a counterclockwise direction to its extreme right hand position to correspondingly decrease the value of current supplied to the heater element 11. At the same time the disk 94 carried by shaft 35 will have been moved to a position wherein the notch 94 in the periphery thereof registers with projection 37 on contact 37. whereby the latter is permitted to separate from contact 37. Opening of contacts 37, 37 effects de-energization of oper ating coil 95 of a relay 95, as will be obvious. This effects closure of contacts 95 and opening of contacts 95, 95 and 95 of said relay. Upon closure of contacts 95 a circuit is completed for the operating coil 59 of relay 59,said circuit extending from line L by conductors 96 and 97 through contacts 62 62 of limit switch 62, conductor 98 through said relay coil 59*, conductor 99 through said contacts 95 and by conductor 100 to line L Relay contacts 59 in closing complete an energizing circuit for winding 66 of motor 30,said circuit extending from line L conoluctor 100 to line L by conductor 96 through the armature of said motor, conductor 101 through said field winding 66, thence through relay contacts 59 and by conductor 100 to line L Motor 30 thereupon operates inv a direction to cause full closed positioning of valve 29, during which operation the traveling nut 70 permits reclosure of contacts 71 opening of said contacts 95 interrupts the energy supply for the entire Wheatstone bridge circuit. In this manner the positive displacement meter 34 is rendered solely eifective for measuring the fluid flow, and the same will remain so pending an increase in the volumetric rate of flow to, say, above 4,000 cubic feet per hour.

Thus Ihave shown a pressure responsive switch 102 having a set of normally open contacts 102 carried by a diaphragm member 102 ,the upper surface of said diaphragm being connected through pipe 102 with branch conduit 31 at the inlet side of meter 34 and the lower surface of said diaphragm being connected through pipe 102 with said branch conduit at the outlet side of said meter 34. Said pressure responsive switch 102 may be so constructed or calibrated as to provide for response thereof to close its contacts 102 when the volumetric rate of flow through branch conduit 31 increases to, say, 4,000 cubic feet per hour.

.the operating coil 81 of relay 81,-said circuit extending from line Ll by conductors 96 and 106 through contacts '71s, '71 of limit switch 71, conductor 107 through said coil 81 conductor 108 through relay contacts 95, and by conductors 109 and .100 to line L Relay contacts 81 upon closure thereof; complete an alternative circuit for motor 30,-said circuit extending from line L by conductor 96 through the armature of said motor, conductors 101 and 110 through the fleld winding 84, and through relay contacts 81 and Motor 30 is thus operated in a reverse direction to effect full open positioning of valve 29,-traveling nut 70 thereupon acting to cause opening of limit switch contacts 71 71 whereby relay coil 81 is de-energized and the contacts 81 thereof reopenedto interrupt the motor circuit connections.

At the same time relay contacts 95 are reclosed to complete the circuit for the current coil of wattmeter 23, heater element 11, and the Wheatstone bridge. xThe electric fluid meter is thus renderedeffective for measuring at least a major portion of .the fluid flow, and the same will remain so effective pending a decrease in the volumetric rate of flow below the aforementioned value of 3,000 cubic feet per hour. In such event the eleto efiect closure of valve 29 and disablingof the electric fluid meter. i.

as compared with the volumetric'rate of flow. at

- which it is cut out of service. This arrangement as aforestated is extremelydesirable sinc'e it' eliminates a hunting? efiect of the measurement controlling elements.

What Iclaim as newand desire to secure by Letters Patent isz a i r a 1 In a fluid meteringsystem, in combination, a main conduit through which a fluid; is adapted to flow, a valve insaid main conduit and poweroperated means for effecting movementof said valveto Open or to closed position selectively, a

branch conduit arranged to by-pass .said valve, a valve in said branch conduit andpower-operated means for effecting movement of said last men tioned valve toopen orto closedposition selem tively, a meter of relatively large capacity located within said main conduit and a meter of relatively small capacity locatedwithin said branch conduit controlvmeans for each of said poweroperatedmeans said control means including means associated; withsaid relatively large meter.

and operableautomatically in response to variationsin the rate of flow of said fluid to effect control of said valves. whereby. said relatively small'meter is selectively. rendered effective or inefiective, and means also associated with said relatively large meter. and operable automatically to renderthejlatter inefiective to measure the flow when said relatively small-,meter' has been rendered eifective.-- r, In a fluid metering system, in combination, a conduit through which a fluid isadapt'ed to flow, an electric. fluid meter "having parts thereof located within saidconduit andnormally operable to indicate and register the total flow of fluid through the latter, a valve in said conduit, power operated means for effectingtmovement of, said valve to open or to; closed position selectively, a branch; conduit arrangedto by-pass said valve, apositive displacement meter of relatively small capacity located within said branch conduit, said power-operated meanslbeing subject to control by a partjof said firstsmentioned meter to efiect closing of saidvalve when they rate of 'fiowdecreases to a predetermined value, whereby said second mentioned meter is renderedeffective for indicating and registering the entire flow of fluid, said first mentioned meter being self-controlled to render ther-latter ineffective for registering. the flow under the conditions last mentioned, and said part of said first mentionedimeter being also operable automatically inresponse to an increase in the rate of flow to a predetermined higher value tocontrol said, power-operated means for effect-- a ing re-opening of, said .valve, whereby said. first mentioned meter isagain rendered effective. ,3. In a fluid metering system, in combination, a meter of relatively large capacity, a main con- 5 duitfin which saidmeter is located, avalvexalso located in saidjmain conduit, a branch conduit arranged to by-pass said va1ve,.a.secon'd .valve located within said branch conduit, a meter of relatively smaller capacity located within said branch conduit, power-operated means for each of said valves, and means including said first mentioned meter for controlling said power-operated means to efiect opening of said second mentioned valve and closure of said'first mentioned valve sequentially when vthe volumetric measuring said 'flow.

rate of'flow of fluid decreases below a predeter mined valueTand' .to efiect' opening cf said first mentioned valvejand closure of said secondmentioned valve sequentially when the volumetric rate of flow of fluid increasesabove a difierent predetermined value, said means also acting to render said first mentioned meterineffectivefor measuring the flow of fluid upon'openingpt said secondmentioned valve. 1

4. In 'a fluid metering system; in combination,

amain conduit through which'a fluid is normally adapted to flow, an electric fluid meter of the I heat-exchange type located within said. conduit, a power-operatedvalve located Within said conduit, a branch conduit communicating at each end thereof with said main conduit and arranged a to by -pasjs said valve; a power-operated'valve' located within said branch conduit, a fluid meter of the, positive displacement type also located within said branch conduit, and means includin'g"said' ,"firs't mentioned meter for controlling said valves to insure open positioning 'of the first mentioned valve [and closed positioning, of

' the second mentioned valve when the volumetric ing of ithe second mentioned valve and closed positioning of the first mentioned valve when the volumetric rateof flow oi said fluid falls below a different predetermined value and to render said first mentioned meter inefiective for 'measuring the flow under the conditions lastimentioned, whereby said'second' mentioned meter is rendered solely effective for measuring said flow.

5. In a fluidmetering system, incombination,

a main conduit through which a gaseous, fluid is adapted to flow, a branch conduit arranged to by-pass a portion of said main conduit, arr electric fluid meter of relatively large capacity located within saidmainconduit, a fluid meter iof relatively small capacity lccated within said branch conduit, 'a valve located withinthe'faforemem I tioned portion of said mainconduit, a valve located within said branch conduit,power-opera ing meansincluding a reversible electric driving motor foreach of said Valves, and control means for said electric driving; motors, -said control means being responsive to a decrease in the'rate of flowof fluid below a predetermined value to effect operation of saidmotors for opening or said second mentioned valve and subsequent j'closfling of said first' 'mentioned valve, said control means also acting under the conditionslast mentioned fluid above .a different, predetermined" Val'u'e to,

effect operation of said motorsjforopeningof said:

first mentioned valve and closing of said second; mentioned valve, said first mentioned meter being simultaneously 1-e dered solely effective 'for 6. In; a, fluid metering system, combination,

l 3 I to render saidflrst mentioned-meter. ineffective aconduit through whicha gaseous fluid is adapted to flow} a valve in saidcondiiit, power-operated means including a reversible electric motor for effecting movement of said valve to openor to closed position selectively, a branch conduit arranged to Icy-pass said valve, a positive displacement meter of relatively small capacity located within said branch conduit andadapted to:

mea'surethe flow of fluid through the latter, an electric fluid meter of the heat exchange type having parts thereof located within said first mentioned conduit, said electric fluid meter being normally adapted to indicate the volumetric flow of fluid therethrough, and means associated with said electric fluid meter and with said power-operated means and adapted to control the latter for effecting closure of saidvalve in response to a decrease in the volumetric rate of flow of fluid through said electric fluid meter below a predetermined value, said last mentioned means being also operable to simultaneously render said electric fluid meter ineffective for measuring the fluid flow, said positive displacement meter being rendered solely effective for measuring the volumetric flow in said first mentioned conduit under the conditions last mentioned.

7. In a fluid metering system, in combination, a conduit through which a gaseous fluid is adapted to flow, a valve in said conduit, power-operated means including a reversible electric motor for efiecting movement of said valve to open or to closed position selectively, a branch conduit arranged to by-pass said valve, a positive displacement meter of relatively small capacity located within said branch conduit and adapted to measure the flow of fluid through the latter, an electric fluid meter of the heat exchange type having parts thereof located Within said first mentioned conduit, said electric fluid meter be ing normally adapted toindicate the volumetric f flow of fluid therethrough,,means associated with said electric fluid meter and with said poweroperated means and adapted to control the latter for effecting closure of said valve in response to a decreaseiin the volumetric rate of flow of predetermined value, said last mentioned means being also operable to simultaneously render said electric fluid meter inefiective for measuring the fluid flow, said positive displacement meter being rendered solely effective for measuring the volumetric flow in said first mentioned conduit under' the conditionslast mentioned, and'associated means operable automatically in response to an increase in' the volumetric rate of flow of fluid through said positive displacement meter above a difierent predetermined value and adapted to control said power-operated means foreffecting re-opening of said valve and for simultaneously rendering said electric fluid meter effective for measuring the volumetric flow of fluid therethrough.

8. In a fluid metering system, in combination, a conduit through'which a gaseous fluid is adaptedto flow, a valve in said conduit, power-operated means including a reversible electric motor for effecting movement of said valve to open or to closed position selectively, a branch conduit arranged to by-pass said valve, a positive dis- 7 placement meter of relatively small capacity located within said branch conduit and adapted to measure the flow of fluid through the latter, an

electric fluid meter of the heat exchange type having parts. thereof located within said first mentioned conduit, said electric fluid meter being normally adapted to indicate the volumetric flow of fluid therethrough, means associated with said electric fluid meter and with said power-operated means and adapted to control the latter for effecting closure of said valve in response to a decrease in the volumetric rate of flow of fluid through said electric fluid meter below a predetermined value, said last mentioned means being also operable automatically to simultaneously render said electric fluid meter ineffective for measuring the fluid flow, said positive displacement meter being rendered solely effective for measuring the volumetric flow in said first mentioned conduit under the conditions last mentioned, said means associated with said electric fluid meter being also operable automatically in response to an increase in the volumetric rate of flow of fluid through said positive displacement meter above a difierent predetermined value and adapted to control said power-operated means for effecting re-opening of said valve and for simultaneously rendering said electric fluid meter effective for measuring the volumetric flow of fluid therethrough, and means controlled by said associated means and operable automatically under the conditions last mentioned to render said positive displacement meter ineffective for measuring any portion of the fluid flow.

9. In a fluid metering system, in combination, a registering meter of relatively large capacity, a main conduit in which said meter is located, a valve also located within said main conduit, a branch conduit arranged to by-pass said valve, a second valve, said second valve being located within said branch conduit, a registering meter of relatively smaller capacity located within said branch conduit, power-operated means including a reversible electric driving motor for each of said valves, electric switching means controlled by a moving part of said first mentioned meter in response to a decrease in the volumetric rate of flow of fluid below a predetermined value to effect full open positioning of said second mentioned valve by its respective driving motor,

means including a limit switch associated with' said second mentioned valve to thereupon initiate operation of the driving motor of the first mentioned valve in a direction to effect full closed positioning of the latter, said electric switching means being also operable by said moving part in response to an increase in the volumetric rate of flow of fluid above a higher predetermined value to effect reverse operation of the driving motor of said first mentioned valve whereby the latter is moved to full open position, means including a limit switch associated with said firstmentioned valve to thereupon initiate operation of the driving motor of the second mentioned valve in a direction to effect full closed positioning of the latter, said large capacity meter having parts thereof responsive to variations in the volumetric 'rate of flow of fluid under all conditions, and said large capacity meter having parts thereof subject to control by said electric switching means whereby said large capacity meter is rendered ineifective for measuring the volumetric flow of fluid except when said first mentioned valve is in open position. 

